In processing logs for various purposes, it is usually necessary to first remove the bark and limbs from the logs. Debarking machines are known for this purpose, and frequently include flail assemblies comprising two or more rotating shafts to which are attached multiple flail chains. If the logs are intended to be processed into chips, it is common for a debarking machine to be located adjacent to, attached to or combined with a log chipping machine. Furthermore, it is desirable to completely remove all bark prior to the chipping process, because bark is considered to be a contaminant in the chips.
In the debarking machine, logs are introduced into the space between the flail assemblies in a direction normal to the axes of rotation of the flail shafts. Typically, the shafts are arranged so that at least one is an upper shaft and another is a lower shaft, although they may be laterally offset from each other. In such a device, the feed line along which the logs are passed through the machine is located between an upper shaft and a lower shaft. In order to remove the bark and limbs from the log, at least some of the flail chains on the upper shaft must reach down along the sides of the log to at least the mid-point. Similarly, at least some of the flail chains on the lower shaft must reach upwardly along the sides of the log to the mid-point. The length of the flail chains on each shaft is dictated by the size of the largest log that is intended to be debarked and the size and positioning of the flail shafts in the debarking machine.
Flail chains may be thirty-six inches long or longer, and are mounted close together. During the debarking operation, the flail chains are subjected to significant stress. As a result, the chain links at the free ends of the flail chains will often break, typically requiring replacement of the flail chains in order to maintain the proper chain length. When the chain links at the free ends of the flail chains break, the other chain links in the flail chain are typically undamaged. Nevertheless, conventional practice requires discarding a flail chain when only one or a few links are damaged. Furthermore, it is a labor-intensive and time-consuming project to change all of the flail chains in a flail assembly.
The upper flail assembly may be mounted on the free end of a pivotable arm structure. In such circumstances, and depending on the relative location of any lower flail assemblies, the action of the flail against the surface of a log may create a reaction force that causes the flail assembly to “float” above the log. An example of such a flail assembly is shown in U.S. Pat. No. 4,719,950 (“the '950 patent”). As described therein, one end of a linear actuator is mounted to the machine frame and the other end is mounted to the pivotable arm structure at an intermediate position between the flail shaft and the pivot mount for the arm structure. This linear actuator is adapted to generate an upwardly directed force against the pivotable arm structure in order to offset only a part of the weight of the flail assembly, so that an additional force is required to raise the flail assembly. This additional force is provided by a gate that is mounted to the pivotable arm structure between the linear actuator and the pivot mount for the arm structure. However, the gate is mounted to extend downwardly at a fixed angle, so that the log being processed, regardless of its diameter, will push against the gate as the log is carried between the upper flail assembly and a fixed lower flail assembly. This gate insures that the shaft of the flail assembly is always a distance above the top of the log being processed that is determined by the configuration of the pivotable arm structure, the location of the linear actuator and the relative angle of the gate. The pivotable arm structure of the '950 patent cannot change the vertical location of the flail assembly shaft independently of the movement generated by the log being processed pushing against the gate. Furthermore, no mechanism is provided in the debarking machine disclosed in the '950 patent to allow for the use of flail chains that are shorter or longer than those shown. Therefore, if flail chains in the flail assembly of the '950 patent become damaged, they will all have to be replaced in order to maintain an efficient debarking operation. Furthermore, if it were deemed desirable to use shorter flail chains in the upper flail assembly of the debarking device of the '950 patent, the flail chains would not reach down far enough to provide for complete bark removal in the logs being processed. If it were deemed desirable to use longer flail chains, the flail chains of the upper flail assembly could damage the adjacent lower flail assembly or other components of the debarking device.
Consequently, it would be desirable if a flail assembly could be provided that would not require replacement of all of the flail chains when the free ends or one or more are damaged. It would be desirable if a flail assembly for a debarking machine could be provided that is adjustable in a vertical direction independently of the diameter of the log being processed. It would also be desirable if a flail assembly for a debarking machine could be provided that can use flail chains of differing lengths, depending on the desired operating conditions, which flail assembly is vertically adjustable without requiring contact between any support structure for the flail assembly and the log being processed.